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41.
Ultra-thin homogeneous oxynitride films are prepared on Si(0 0 1). The Si surface is cleaned in UHV by heating (flashing) and is exposed to different pressures of N2O at altered temperatures. Thus oxynitride layers of different thickness and different properties are grown depending on the N2O pressure and the Si temperature. This is illustrated by a schematic diagram. The properties of the different oxynitride layers were studied by a combined photoemission electron microscopy (PEEM) and photoelectron spectroscopy (PES) investigation using highly monochromatic synchrotron radiation. The amount of oxygen and nitrogen incorporated in the oxynitride layers is determined from the PES measurements. The typical surface morphology for different preparation conditions is shown in PEEM images. 相似文献
42.
The rate of dissolution and growth of settling crystals of spinel was measured optically in a borosilicate melt that was pre-heated at a temperature above liquidus to erase the effects of previous history. The Hixson-Crowell equation, which is based on Fick's first law, was used to determine mass-transfer coefficients (kH) for dissolution and growth; both were found to fit the same Arrhenius function of temperature (T). An attempt was made to estimate the diffusion coefficient (D) and the concentration-boundary-layer thickness (δ). The calculated values of δ compared well with experimental results and observations. The D vs. T function was similar to a literature function obtained for the dissolution of magnetite in sodium disilicate glass. 相似文献
43.
EzzEldin Metwalli 《Journal of Non》2003,317(3):221-230
Copper oxidation states, structure and properties of xCuO · (50-x)PbO · 50B2O3 glasses were investigated. Both infrared (IR) and 11B magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopies were employed to determine the tetrahedral BO4 fraction in the glasses as a function of CuO content. IR study indicates that the replacement of Pb2+ by Cu2+ ions increases the BO3 units by converting BO4- containing groups into ring type metaborate groups. The oxidation states of copper ions in the glasses have been studied using both X-ray photoelectron spectroscopy (XPS) and the wet chemical method. For high CuO containing (?30 mol%) glasses, high Cu+ ion concentrations (Cu+/Cutot.>0.3) result in a relatively slow disproportionation of B4-containing groups because of the small coordination number of Cu+ compared to Cu2+ ions. Effects of both glass structure and redox states of copper ions on glass properties including density, Vickers’ hardness, coefficient of thermal expansion, and chemical durability have been discussed. 相似文献
44.
Conventional photocycloaddition of 1,4-dihydropyridines does not afford novel head-to-head 3,6-diazatetraasteranes. Herein, we describe a highly regioselective method to synthesize 3,6-diazatetraasteranes via an intramolecular photodimerization of 1,4-dihydropyridines. First, the 1,4-dihydropyridines were tethered by phthaloyl to direct a proximate parallel arrangement in head-to-head orientation by the rotation of CC single bonds in solution. An intramolecular [2 + 2] photocycloaddition proceeded subsequently to give desired 3,6-diazatetraasteranes in high yield (92–97%) and excellent regioselectivity. Furthermore, two different 1,4-dihydropyridines can also be regiocontrolled by this strategy and produce polysubstituted 3,6-diazatetraasteranes via a cross-photodimerization in a concise and efficient way. In addition, this approach can provide direct access to other polysubstituted polyhedron scaffolds from 1,4-dihydropyridine analogues. 相似文献
45.
Wen-Bo Lan Sha Gao Ying-Wu Lin Guo-Wen Peng 《Journal of Coordination Chemistry》2016,69(18):2775-2784
Uranyl–salophen (U–S) complexes, as modified by unilateral benzene and coordinated with cyclohexenones substituted by methyls or fluorines in E/Z-types, were investigated using density functional theory calculations at the level of B3LYP/6–311G** basis set. The results indicated that the O of substituted cyclohexenones could coordinate with U of the asymmetric U–S complexes. When the C=C bond of cyclohexenones was located upward in the twisted salophen plane, the binding energies of the cyclohexenones to the asymmetric U–S and Wiberg bond indices (WBIs) of carbonyl oxygen to uranium (U–O) were higher than those of the C=C bonds located downward. It could be concluded that when cyclohexenones were coordinated to the asymmetric U–S, the major products would be the complexes in which the C=C bond of cyclohexenones locates upward in the configuration. Binding energies of the E-type substituted cyclohexenones to the asymmetric U–S were higher than those for the Z-type ones. 相似文献
46.
A new eremophilane sesquiterpene, capnodiumone (1), along with five known eremophilane sesquiterpenes (2–6) and eight other compounds (7–14), have been isolated from a mangrove-associated fungus Capnodium sp. SZ-F22. The chemical structures were elucidated on the basis of extensive spectroscopic analysis. The broth extract of the fungus exhibited a good inhibitory effect on the mycelium growth against Fusarium graminearum at 100 μg/mL, however, all the 14 compounds showed no expected antifungal activity. The probable reasons were discussed. 相似文献
47.
A new isoflavone glycoside, (?)-tuberosin-3-O-β-D-glucopyranoside (1), along with 10 known compounds 1a-10, was isolated from Pueraria alopecuroides. Their structures were determined on the basis of spectral data including 1D and 2D NMR and HREIMS. These compounds were isolated from this plant for the first time. 相似文献
48.
Proanthocyanidins (PA) in Senna alata leaves were investigated by thiolysis with benzyl mercaptan, LC–MS and NMR and consisted of almost pure propelargonidins with <6% procyanidins, had B-type linkages and a mean degree of polymerisation of three. Epiafzelechin was the major flavan-3-ol subunit (>94%) and epicatechin a minor constituent (6.4%) in residual PA and mainly detected as an extension unit. 相似文献
49.
The surface of a high quality soda-lime silicate glass is found to be inhomogeneous, consisting of nanometer-high ridges that extend for tens of microns. Exposure to mild and aggressive environments results in an increase in the ridge heights as they dissolve much more slowly than the rest of the glass. The ridges also exhibit enrichment of sodium, magnesium, aluminum and oxygen. The parallel nature of the ridges suggests that they originate from compositional heterogeneity during the glass processing. 相似文献
50.
H. Nohira W. TsaiW. Besling E. YoungJ. Petry T. Conard W. VandervorstS. De Gendt M. HeynsJ. Maes M. Tuominen 《Journal of Non》2002,303(1):83-87
The atomic layer chemical vapor deposition (ALCVD) deposited Al2O3 and ZrO2 films were investigated by ex situ X-ray photoelectron spectroscopy. The thickness dependence of band gap and valence band alignment was determined for these two dielectric layers. For layers thicker than 0.9 nm (Al2O3) or 0.6 nm (ZrO2), the band gaps of the Al2O3 and ZrO2 films deposited by ALCVD are 6.7±0.2 and 5.6±0.2 eV, respectively. The valence band offsets at the Al2O3/Si and ZrO2/Si interface are determined to be 2.9±0.2 and 2.5±0.2 eV, respectively. Finally, the escape depths of Al 2p in Al2O3 and Zr 3p3 in ZrO2 are 2.7 and 2.0 nm, respectively. 相似文献